Fundamental requirements for safety

Fundamental requirements for safety

Session 7

Contents

7.1    The scope of the wiring regulations

7.2    The object of the regulations

7.3    Fundamental requirements for safety

7.3.1 A discussion of the fundamental requirements

Aim

The aim of this session is to teach you the fundamental requirements of safety in an electrical installation.

Specific objectives

At the end of this session you will be able to:

(i)         State the scope of the wiring regulations briefly

(ii)        State the object of the regulations

(iii)       State briefly the 20 Regulations relating to the fundamental requirements of safety

(iv)       Briefly discuss the relevance of the regulations of chapter 13.

Introduction

In the previous lesson we learnt that the Part I of the Regulations gave the overriding requirements. What were they? They were the scope, object and the fundamental requirements of safety.

7.1    The scope of the wiring regulations

The Wiring Regulations, like any other design manual, has a scope. For example, it will not give any regulations as to the design of buildings, as this is completely outside its scope. Others may not be that obvious, so that chapter 11 of the Regulations specify its scope and exclusions. Two of the Regulations are: Regulation 11-1 states that these Regulations relate principally to the design, selection, erection, inspection and testing of electrical installations, whether permanent or temporary, in and about buildings generally.

Regulations 11-2 states that only installations utilizing 'Extra-low-voltage' and 'low voltage' nominal voltage ranges are dealt with in the Regulations. However certain installations operating at voltages exceeding low voltage are also covered where they relate to discharge lighting and electrode boiler.

7.2    The object of the regulations

The object and Effects of the Regulations are specified in chapter 12.

Regulation 12-1 states that these Regulations are designed to provide safety, especially from fire, shock and burns.

Regulation 12-2 states that the Regulations are intended to be cited in their entirety if referred to in any contract, and that they are not intended to take the place of a detailed specification or to instruct untrained persons or to provide for every circumstance. Installations of a difficult or special character will require the advice of a suitably qualified electrical engineer.

The remaining Regulations in this chapter deal with the relationship with statutory regulations; use of established materials, equipment & methods; new materials, inventions and designs; assessment of new techniques and installations in premises subject to licensing.

It is also stated that Notes to these regulations do not form part of the Regulations but are given for guidance.

7.3    Fundamental requirements for safety

Chapter 13 of the Regulations give the fundamental Requirements for safety. It is worth noting that the subsequent chapters of the Regulations are themselves a description of methods of compliance with chapter 13. This chapter has been written in broad terms to allow room for interpretation in particular cases. However, chapter 13 is normally invoked only where it is intended to adopt a practice not recognized in the later chapters.

Question

In several of the Regulations in this chapter, the phrase 'so far as is reasonably practicable' is used. Does it mean that a lot of departures from the usual practice, stipulated in the later chapters, is permitted?

Discussion

No. The methods described in the later chapters are reasonably practical in most cases and should only be departed from, where an unusual practice is proposed which makes certain requirements unnecessary or inappropriate. However, it is to be noted that if the proposed practice results in a degree of safety less than that provided by compliance with the later chapters, it is unlikely to be judged as having complied with 'so far as is reasonably practicable'.

Thus it may be said that chapter 13 of the Regulations includes 20 short Regulations which cover, in very general terms, all the material included elsewhere in the Regulations. Failure to comply with chapter 13 will thus mean that a supply Authority will be able to withhold connection, or may arrange disconnection, of the supply mains to the installation concerned. It is thus important to understand thoroughly these 20 Regulation which are given below under appropriate subtitles.

Workmanship and materials

13-1     Good Workmanship and proper materials shall be used.

General

13-2     All equipment shall be constructed, installed and protected, and shall be capable of being maintained, inspected and tested, so as to prevent danger so far as is reasonably practicable.

13-3     All equipment shall be suitable for the maximum power demanded by the current-using equipment when it is functioning in its intended manner.

13-4     All electrical conductors shall be of sufficient size and current carrying capacity for the purposes for which they are intended.

13-5     All conductors shall either-

(i)   Be so insulated, and where necessary further effectively protected, or

(ii)  Be so placed and safeguarded, as to prevent danger, so far as is reasonably practicable.

13.6     Every electrical joint and connection shall be of proper construction as regards conductance, Insulation and mechanical strength and protection.

Overcurrent protective devices

13-7     Where necessary to prevent danger, every installation and every circuit thereof shall be protected against overcurrent by devices which

(i)         will operate automatically at values of current which are suitably related to the safe current ratings of the circuit, and

(ii)        are of adequate breaking capacity and, where appropriate, making capacity, and

(iii)       are suitably located and are constructed so as to prevent danger from overheating, arcing or the scattering of hot particles when they come into operation and to permit ready restoration of the supply without danger.

Note

Where the supply undertaking provides switchgear or fuse gear at the origin of the installation it may not be necessary to duplicate the means of overcurrent protection for that part of the installation between its origin and the main distribution point of the installation where the next step for overcurrent protection is provided.

Precautions against earth leakage and earth fault currents

13-8     Where metalwork of electrical equipment, other than current-carrying conductors, may become charged with electricity in such a manner as to cause danger if the insulation of a conductor should become defective or if a fault should occur in any equipment-

(i)   The metalwork shall be earthed in such a manner as will cause discharge of electrical energy without danger, or

(ii)  Other equally effective precautions shall be taken to prevent danger

13-9     Every circuit shall be arranged SO as to prevent the persistence of dangerous earth leakage currents.

13-10   Where metalwork is earthed in accordance with Regulation 13-8(i), the circuits, concerned shall be protected against the persistence of dangerous earth fault currents by -

(i)   The overcurrent protective devices required by Regulation 13-7, or

(ii)  A residual current or voltage operated device or equally effective device.

The method described in item (ii) above shall be used whenever the prospective earth fault current is insufficient to cause prompt operation of the overcurrent protective devices.

13-11   Where necessary to prevent danger, where metalwork of electrical equipment is earthed for compliance with Regulation 13-8(i) and is accessible simultaneously with substantial exposed metal parts of other services, the latter parts shall be effectively connected to the main earthing terminal of the installation.

Position of protective devices and switches

13-12   No fuse, or circuit breaker other than a linked circuit breaker, shall be Inserted in an earthed central conductor, and any linked circuit breaker inserted in an earthed neutral conductor shall be arranged to break also all the related phase conductors.

13-13   Every single pole switch shall be inserted in the phase conductor only, and any switch connected in an earthed neutral conductor shall be a linked switch and shall be arranged to break also all the related phase conductors.

Isolation and switching

13-14   Effective means, suitably placed for ready operation shall be provided so that all voltage may be cut off from every installation, from every circuit thereof and from all equipment, as may be necessary to prevent or remove danger.

Note

Where the supply undertaking provides switchgear or fusegear at the origin of the installation it may not be necessary to duplicate the means of isolation for that part of the installation between its origin and the main distribution point of the installation where the next step for isolation is provided.

13-15      For every electric motor an efficient means of disconnection shall be provided which shall be readily accessible, easily operated and so placed as to prevent danger.

Accessibility of equipment

13-16   Every piece of equipment which requires operation or attention by a person in normal use shall be so installed that adequate and safe means of access and working space are afforded for such operation or attention.

Precautions in adverse conditions

13-17   All equipment likely to be exposed to weather, corrosive atmospheres, or other adverse conditions, shall be so constructed or protected as may be necessary to prevent danger arising from such exposure.

13-18   All equipment in surroundings susceptible to risk of fire or explosion shall be so constructed or protected, and such other special precautions shall be taken, as may be necessary to prevent danger.

Additions and alterations to an installation

13-19   No additions or alterations, temporary or permanent, shall be made to an existing installation, unless it has been ascertained that the ratings and the condition of any existing equipment (including that of the supply undertaking) which will have to carry additional load is adequate for the altered circumstance and that the earthing arrangements are also adequate.

Inspection and testing

13-20   On completion of an installation or an extension or alteration of an installation, appropriate tests and inspection shall be made, to verify so far as reasonably practicable that the requirements of Regulations 13-1 to 13-19 have been met.

7.3.1    A discussion of the fundamental requirements

Regulation 13-1 gives the first and foremost requirement of safety, namely that good workmanship and proper materials are essential, and cannot be compromised. The group of regulations 13-2 to 13-5, taken together are designed to ensured maintainability, limit the rise in temperature throughout the installation, prevent direct contact and guard against mechanical failure or damage. For example, the PVC sheath on cables is further protection intended to prevent damage to the insulation. Conduits through which cables are drawn serve the same purpose. Regulation 13-7 lays down the co-ordinated characteristics and the overload and short-circuit protection.

The group of regulations 13-8 to 13-11 gives the precautions against earth leakage and earth fault current. We see that the use of an overcurrent device alone for the protection against the persistence of dangerous earth fault currents is permitted only where the prospective earth fault current is sufficient to cause prompt operation of that device. The voltage operated earth leakage circuit breaker (ELCB) (commonly called by electricians in Sri Lanka in the past as the Trip Switch) has been an effective means of limiting the earth terminal voltage in the event of a fault. However by far the best means is the Residual current Circuit Breaker (RCCB) (or sometimes wrongly referred to as the current operated earth leakage circuit breaker). The present regulations, do not merely recommend the use of RCCB, they make their use obligatory where life and limb are at risk.

Regulations 13-12 and 13-13 tell us the vital need to maintain the continuity of the neutral. If for some reason the neutral is broken and disconnected and not the phase conductor, the user may get the false impression that the circuit is dead and try to repair it, while in actual fact it is still live. For the same reason no switch is permitted on the neutral alone. Regulations 13-14 and 13-15 tell us about the isolation requirement, especially for motors. The importance of safe and proper access to equipment which requires attention in normal use is stressed by regulation 13-16, where as regulations 13-17 and 13-18 deal with the need for suitable equipment for coping with adverse conditions and in surroundings where the risk of fire or explosion is great. Further care should be taken in choosing equipment for buildings close to the sea and where the fire hazard is unusually great.

Regulation 13-19 deals with additions and alterations and tells us that this is permitted only where adequate excess ratings are available and adequate protection is available.

Regulation 13-20 deals with the inspection and testing that must be carried out after completion. Just because inspection and testing is going to be done at the end to check on the fundamental requirements, we cannot ignore the prime requirement of good workmanship and proper materials. One is not an alternative to the other. 

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